Tuesday, June 22, 2010

POORWILL, BEAUTIFUL BIRD OF THE NIGHT



Common Poorwills (Phalaenoptilus nuttallii) are widely distributed throughout western North America, but how many of you have seen one? They are strictly nocturnal and perfectly camouflaged in their daytime resting sites.

On a recent early June trip to eastern Washington, we drove up Robinson Canyon, west of Ellensburg, in the evening. Robinson Canyon is a riparian oasis in the midst of sagebrush shrub-steppe and ponderosa pine woodland. We arrived at about 8 pm at a gate in the fence that encloses part of the L. T. Murray Wildlife Recreation Area. As it got darker and darker, we enjoyed the sights and sounds of the local songbirds going to bed. A Western Wood-Pewee sallied after insects later than we expected a flycatcher to be out and about. Another one sang its dusk song nearby.

But we were after more elusive game. As it got dark, our quarry began to stir. At 9:12 pm, a poorwill called its name from the nearby shrubby and rocky hillside. Several others followed in succession, until a steady chorus of melodious ‘poorwill . . . . . . poorwill . . . . . . poorwill’ resounded from the hillsides. At 9:27 pm, we saw the silhouette of a bird flitting across the road. We started the car and pulled away from the roadside at 9:30, when it was entirely dark.

Very soon the headlights picked up a poorwill resting on the road. This bird eats large moths and beetles that it sees against the sky as it rests on open ground, and roads through its habitat often represent the most open terrain for a foraging bird, so we were taking advantage of this long-known way to get a look at poorwills. Their eyes shine brilliant orange in the light of the headlights.

Seven poorwills flushed from the road in the three miles of road we drove, and fortunately, as the goal of the evening was to get photos, two of them remained on the edge as we slowly drove by them, allowing shutters to click to complete satisfaction. The huge eyes, tiny beak (but the gape extends back behind the eyes), and tiny feet (almost useless for locomotion) were visible at close range.

Trying to find them in the daytime is another story. They sometimes perch right out in the open, on broken ground or rocks, but seeing one before you flush it is an art or science that is beyond me. I once chased one around, trying to get photos of it in broad daylight, and I could never see it before I flushed it, sometimes within a few meters. Their camouflage, I thus conclude, is perfect. Joe Marshall, an ornithologist who spent a lifetime studying nocturnal birds, called the Common Poorwill the most beautiful bird.

But poorwills are much more interesting than just being big-eyed, big-mouthed nocturnal insectivores. They were the first bird to be discovered “hibernating,” in deep torpor in a south-facing rock crevice in southern Arizona. Amazingly, this species is still the only bird known to spend long periods in torpor, remaining completely inactive for days during periods of low temperatures during winter. At those times, body temperature can drop to 5°C, oxygen consumption to <10% of normal. This has the earmarks of true hibernation, but it is not. Instead, it is a day-to-day phenomenon, not the deep winter sleep of marmots and other mammals. Poorwills may enter this state at any time of low temperatures, an energy-saving strategy that allows them to cope with periods when no insects are out and about.

Dennis Paulson

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